Throughout the text, a mechanical member will be said to be magnetic if the material that constitutes it has a relative magnetic permeability greater than 1. Such magnetic materials are for example ferromagnetic materials (iron, nickel, steel, cobalt, etc).
A permanent magnet is a mechanical member that is magnetised permanently and itself generates a magnetic field.
Electromagnetic pumps with an oscillating magnetic piston are used at the present time in numerous applications, including coffee machines, automatic dispensers, steam ironing units, irrigation systems, air conditioning systems, the automobile industry, etc.
In these various applications, the use is known of an electromagnetic pump comprising:                a hollow tubular body extending along a longitudinal direction,        a magnetic piston mounted so as to move longitudinally inside the hollow tubular body, the piston being itself hollow and traversing longitudinally,        a coil supplied by a half-cycle rectified alternating current forming an electromagnet,        a fluid-suction chamber delimited by a fluid inlet in the hollow tubular body and the movable magnetic piston,        a fluid-exhaust chamber delimited by a fluid exhaust outlet in the hollow tubular body and the movable magnetic piston,        a working spring provided in the suction chamber and extending between the fluid inlet and the movable magnetic piston,        non-return valves mounted at the inlet and outlet of the discharge chamber.        
Such a pump enables fluid to be pumped by alternating axial movements of the piston under the effect of the magnetic field created by the electromagnet. This is because, in accordance with the physical principle of maximum flux, the magnetic piston moves spontaneously under the effect of a magnetic field so that the magnetic flux passing through it is maximum.
Thus, at each current amplitude in the coil, the piston is moved counter to the working spring, housed in the suction chamber. This movement leads to an increase in the volume of the discharge chamber and reducing the pressure therein, which causes the non-return valve of the discharge chamber inlet to open. The fluid can then pass from the suction chamber to the discharge chamber through the hollow piston.
When the current in the coil of the electromagnet decreases and then becomes zero, the electromagnetic force disappears and the working spring can push the piston in order to move it in the opposite direction. This movement creates an increase in pressure in the discharge chamber, which leads to the closure of the inlet non-return valve and to the opening of the outlet non-return valve. The fluid can then leave the discharge chamber. In addition, the movement of the piston leads to an increase in the volume of the suction chamber and therefore to a reduction in the pressure, which leads to the suction of fluid into the suction chamber. The pump is then ready to undergo a new current cycle.
One of the drawbacks of these pumps of the prior art lies in low hydraulic performance—in particular throughput and suction.
Another drawback of these pumps is that they have a low starting power, which impairs their overall robustness. In particular, the pistons of these pumps do not have a good capacity to unstick in the event of blocking.
Another drawback of these pumps is that the piston must be fixed precisely with respect to the air gap, in order to have stable hydraulic performance, which requires the use of parts having very precise tolerances.
Another drawback of these pumps is that they cannot be directly connected to the mains.